1. Field of the Invention
This invention relates generally to network protection systems and more particularly to protection schemes for such systems to provide protection switching for optical signals in an optical transport network
2. Description of the Related Art
For high-reliability signals, such as those used in telecommunications and data communications, duplicate versions of the signal are routed through the network, e.g., optical such as a synchronous optical network (SONET), via different paths, referred to as a working path and a protection, or standby, path. Thus for a given signal transmitted on one path, the duplicate path will be the complement of the first path, e.g., if the first path is a working path then the second path is the protection path, or vice versa. Such duplicate paths are created at initialization to capture network resources for routing the signal through different nodes and/or different fiber links in the network. In this manner, if a failure occurs in a given path, e.g., a laser failure in a node or a fiber breakage between nodes, then a duplicate version of the signal already exists in the network, and only requires a simple switching from one path to the other at a junction point in order to continue the progress of the signal. While the cost of duplicate routing is the consumption of bandwidth, the benefit is protection from a loss of service.
There are multiple types of protection schemes, including mesh, dedicated, and shared. In a shared protection scheme, the signal is transmitted on only one path, e.g., the working path, while the complementary path, e.g., the protection path, is simply set up for one or more signals without actively transmitting a signal on the path until a fault arises in the one or more working path signals. In this manner, the shared redundant routing conserves routing bandwidth and allows the protection path to be shared among multiple working channels. However shared redundant routing may suffer from longer switchover times because of latency in the transmission of control information. Dedicated redundant routing overcomes these limitations by constantly communicating the signal on both the working and protection path, albeit at the cost of consuming bandwidth.
Both the working and protection path will provide a signal received at a node. However, the signal from only one of those paths is chosen for transmission out of the node, e.g., to either a downstream node in the network, to an adjacent network, or to an out-of-network client. The path whose signal is chosen for subsequent transmission out of the node is referred to as a so-called active path. The working path may initially be designated as the active path, but the protection path may subsequently be assigned the active path state, leaving the working path in an inactive state. This switching, referred to as Automatic Protection Switching (APS), may toggle the active state back and forth between the working and protection path as necessary to reliably transmit the signal in the network.
In order to minimize disruption of the signal, a need arises to provide the APS function as quickly and reliably as possible. Every millisecond of interruption means the loss of potentially valuable data. If a control-plane based communication system for optical communication networks, or systems, utilizes software-software communication with a software protocol stack, e.g., on an Ethernet infrastructure, for protective, or active, switching, then multiple software layers may be required for message generation, transmission, receipt, and interpretation. In turn, multiple software layers in a software-based protective switch engine may be slower and less predictable than hardware based protective switching architecture. Consequently, a need arises to overcome the latency and unpredictability of a software-software based APS implementation.
If a system utilizes a control scheme that is “hard-wired” or based solely on a hardware mechanism for controlling APS, it might provide faster switching than software based solutions. However, a typical limitation with hardware solutions might arise, that of inflexibility in the choices of which ports are associated in the protection scheme and which protection algorithms are applied. Consequently, a need arises for a fast protection based switching that also has flexibility in signal routing and protection algorithms.
These aforementioned needs arise for traditional electronic based communication networks, as well as optical based networks, such as optical dense or coarse wavelength division multiplexing (DWDM) (CWDM) systems.